There are many types of systems in which solenoid actuated valves are utilized. Solenoid actuated valves, such as that described in U.S. Pat. No. 5,398,724, are particularly well suited for use in controlling the delivery of gaseous fluids in engine applications. For example, such a valve can be placed between a gaseous fuel inlet region and an air intake region of a spark ignited internal combustion engine or dual fuel engine.
A dual fuel engine can typically operate in two modes. In a strictly liquid fuel mode a liquid fuel, such as diesel fuel, is injected directly into an engine cylinder or a precombustion chamber as the sole source of energy during combustion. In a dual fuel mode a gaseous fuel, such as natural gas, is mixed with air in an intake port of a cylinder and a small amount of diesel fuel is injected into the cylinder or the precombustion chamber in order to ignite the mixture of air and gaseous fuel.
Regardless of the application in which such solenoid-actuated valves are utilized, it is sometimes possible for such valves to malfunction. For example, a solenoid actuated valve typically includes a movable plate and a stationary plate or seat. If particulate impurities in the fuel get trapped between the movable plate and the stationary plate, the plates will be unable to move close enough together to prevent unintended fuel flow. Other types of impurities may cling to the moving components of the valve, thereby slowing movement of the plates. Further, in some cases an air pressure differential across the valve may become great enough to impede or prevent opening and closing of the valve. In many applications, such as in engine applications, it is desirable to know when problems such as these exist.
Automatic feedback and control systems for engines often include inductive or potentiometric sensors connected to a control unit to detect measurable quantities. Such measurable quantities include, for example, the position of the throttle control of an engine, the position of the control rod of a diesel injection pump, or the position of an accelerator pedal. During the operational life of the device being monitored, drift effects, due to mechanical wear of the control unit (including any associated limit stops) or contact resistance in the connecting lines leading to the control unit, for example, can corrupt the measured values. Reducing the influences of such effects often entails costly construction or regular servicing and adjustment of such sensors.
Prior systems provide indirect means for diagnosing a faulty or frozen fuel admission valve. U.S. Pat. No. 5,487,372 discloses a fuel system apparatus for detecting deterioration of the response of an air control valve by measuring air pressure at the upstream and the downstream sides of an air control valve disposed in an air passage. U.S. Pat. No. 5,666,924 discloses a device for diagnosing a malfunction of a gas-processing device including a valve, a misfire detector, and an O.sub.2 sensor. The device monitors pressures in a fuel tank when the valve is opened and closed along with changes in the air/fuel ratio to determine when a malfunction occurs. U.S. Pat. No. 5,617,337 issued to Eidler et al. teaches a method and device for monitoring the functions of a sensor to determine whether the sensor is operating within predetermined tolerances during various operating states of an internal combustion engine. The method and device disclosed in the Eidler et al. patent require storing a measured value as a reference value when one of a specified operating states exists at a first time and comparing subsequent values. One of the specified states must include a control mechanism being positioned at an end limit stop of a control mechanism. Thus the Eidler et al. method and device are not usable in situations where an end limit stop is not reached.
When quantities that indirectly indicate the position of the valve are used to monitor operation of the valve, there is a risk of misdiagnosing the cause of the problem. For example, a fully functional valve may be replaced if exhaust temperature is used to diagnose a faulty or frozen valve since there are no means to determine whether the deviation in temperature is due to a faulty valve or some other problem. None of the foregoing devices disclose means for directly measuring the position of the valve in a solenoid gaseous fuel admission valve to determine whether the valve is operating properly.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.